I was driving home from work one evening and saw a billboard (I don't remember about what), and a drinking song was on the radio, and the combination of the two created the line "180 Proof, 180 degrees from the truth". Sometime later the "double homicide/suicide" idea for the rest of the song came to me.

180 Proof

It’s been a long hard day
So you just stop off to see your friends
To have a few drinks and a laugh or two
And see if the waitress catches your eye again

Your wife’s waiting for you
Wondering why you don’t come home
She hates the waiting more than the lying
Knowing what you’re doing and feeling so alone

[Chorus]
It’s just a little glass
But it helps make the lying last
So you put out the pain with 180 proof
You know she knows you’re lying
And you don’t care she’s crying
With 180 proof, 180 degrees from the truth

Your children are in bed
And your wife has cried herself to sleep
She dreams of your love that she’s missed for years
And wishes she could stop you and your heart she could keep

She hears your footsteps fall
She reaches in the drawer by the bed
She smells perfume and the whiskey on your breath
The cold steel in her hand shatters her silence with lead

[Chorus]
It’s just a little glass
But it helps make the lying last
So you put out the pain with 180 proof
You know she knows you’re lying
And you don’t care she’s crying
With 180 proof, 180 degrees from the truth

The sheriff found you both there
Your children were taken away
One stone, two birds, one shot, two broken hearts
Now the pain and the heartache are handed down to stay

[Chorus]
It’s just a little glass
But it helps make the lying last
So you put out the pain with 180 proof
You know she knows you’re lying
And you don’t care she’s crying
With 180 proof, 180 degrees from the truth